Pulse jet apparatus



Nov. 8, 1960 W, DRR ETAL 2,959,214

PULSE JET APPARATUS Filed March 21, 1955 s sheets-sheet 1 Q w f-v.

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m 1, L 1 4 E l f@ Q Q lb INVENTOR W. DRR ET AL Nov. 8, 1960 PULSE JET APPARATUS 3 Sheets-Sheet 2 Fled March 21, 1955 l, lNvEN-'roR luf/.Her Burr, Franz n, Haag,

Nov. 8, 1960 w. DURR ETAL PULSE JET APPARATUS 3 Sl'xeets-Shee'k'I 3 Filed March 21, 1955 lNvENToR (daher u.rr, Frfmz Ha am! Bernhard E. Sfr/#marrer /wA-CAMA S. Sw' K .uw il .ferent chemicals but also with different apparatus.

United States Patent O PULSE JET APPARATUS Walter Drr, Franz A. Haag, and Bernhard E. Strittmatter, Uberlingen, Germany, assignors to Swingfre Limited, Nassau, Bahamas Filed Mar. 21, 1955, Ser. No. 495,654

Claims priority, application Germany Nov. 15, 1954 6 claims. (ci. 15s-4) The present invention relates to pulse jet apparatus for spraying and atomizing liquids.

More particularly, the present invention relates to apparatus for spraying and atomizing liquids such as insecticides, fungicides, and liquids to provide mists for protecting plants against frost. Furthermore, the invention relates to an apparatus of this type which is portable, which is not dangerous to operate, and which may be used for disinfecting closed rooms as Well as for spraying fruit trees and for laying mists over an entire culture. It is conventional to atomize liquid insecticides by feeding them into the exhaust tube of an internal combustion engine. The liquid thus introduced into such an exhaust tube is broken up into ine drops by the combined action of the heat and the pulsating stream of gas in the exhaust tube, and such tine drops are exhausted to the atmosphere with the exhaust gases. Furthermore, it is already known to atomize a liquid by introducing it into the exhaust tube of a pulse jet engine wherein the pulsating stream of exhaust gases also breaks the liquid up into fine droplets.

It is an object of the present invention to provide an Y an improved pulse jet engine of an exceedingly simple a' construction which may be operated without danger and which may be started without danger.

Another object of the present invention is to provide a nozzle structure which is particularly suited for introducing the liquid to be atomized into the exhaust tube of the pulse jet engine.

Up to the present time farmers have been compelled vto protect different plants and the like not only with dif- Thus, 'for example, in order to spray fruit trees in the spring time Ait is necessary to use an apparatus which provides relatively large droplets, so that these large droplets may settle on the leaves and twigs of the fruit trees and remain effective thereon for a long period of time. On the other hand, in order to combat flying insects in the summertime as well as to disinfect store rooms and to protect stored grain it is necessary to use an apparatus which produces a dense mist composed of much finer droplets so that the chemical material will remain suspended for a longer period of time and will iind its way to all parts of the material to be protected. Finally, in order to providemists which will protect against frost in the wintertime, it is necessary to use a third apparatus which forms an extremely dense mist composed of extremely tine droplets which remain suspended in the atmosphere for many hours and which reflect as much heat from the ground as possible.

An additional object of the present invention is to provide a single apparatus capable of being used for all of the purposes mentioned above only by changing the is shaped to form a cyclone.

f2,959,214 Patented Nov. 8, 1960 lCe outlets provided at the outlet end of the exhaust tube of the pulse jet engine. Thus, an object of the present invention is to provide an apparatus of the above type with interchangeable outlets suitable for different purposes.

Still another object of the present invention is to provide a means for cooling the exhaust gases of a pulse jet engine so that breakdown and decomposition of the liquid to be atomized is prevented.

`A still further object of the present invention is to provide a means for preheating the liquid to be atomized so as to reduce its viscosity and thereby make it easier to atomize.

With the above objects in view the present invention mainly consists of a pulse jet engine which includes a combustion tube forming the combustion chamber of the engine, an exhaust tube communicating with and extending coaxially from the combustion tube, and a supply tube communicating tangentially with the combustion tube for supplying a combustible mixture to the interior of the combustion chamber.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of speciiic embodiments when read in connection with the accompanying drawings, in which:

Fig. 1 is a partly sectional, partly diagrammatic side elevational view of an apparatus constructed in accordance with the present invention;

Fig. 2 is an enlarged sectional illustration of part of the structure of Fig. 1 taken along line 2 2 of Fig. 1 in the direction of arrows;

Fig. 3 is an enlarged fragmentary sectional illustration of the nozzle structure at the outlet endfof the discharge tube of the pulse jet engine;

Fig. 3a fragmentarily illustrates a different embodiment of part of the nozzle structure of Fig. 3; and

Figs. 4a-4c respectively show fragmentarily and partly in section different attachments which may be joined to the outlet end of the exhaust of the pulse let engine.

Referring to Fig. l, it will be seen that the pulse jet engine of the invention includes an elongated straight exhaust tube 1 whose outlet end, shown at the left in Fig. 1, carries a discharge device 2 described below and whose right end, as viewed in Fig. 1, is joined to acombustion tube 3 which forms a wall means which defines the combustion chamber for the engine. As is evident from Fig. 1, disch-arge tube 1 communicates coaxially With the interior of combustion tube 3, and this tube 3 Thus, it is evident from Fig. 1 that the combustion tube 3 includes a cylindrical right end portion, as viewed in Fig. 1, and a frustoconical portion joined at its larger open end t-o the cylindrical portion and at its smaller open end to the discharge tube 1. A supply tube 4, for supplying a combustible mixture to the interior of combustion tube 3, communicates tangentially with the cylindrical portion of combustion tube 3, as shown in Fig.k2. The supply tube 4 supplies a fuel-air mixture to the interior of combustion tube 3, and the components of this mixture are mixed Within the tube 4. Thus, the tube 4 carries an air inlet 5' provided with a non-return valve S which prevents air from moving from the interior of tube 4 outwardly through the inlet 5', and a combustible fuel is introduced into the tube 4 through a conduit 6 which communicates with the interior of the tube 4 as indicated in Figs. l and 2.

The non-return valve 5 is constructed as shown in Fig. 2 of U.S. Patent No. 2,701,950 of Ludwig R. I-luber and Franz A. Haag, this non-return valve providing an adjustment of the resistance to the flow of air. The fuel supply structure 6 is constructed according to Fig. 4 of U.S. Patent No. 2,719,580 of Franz A. Haag and Ludwig R. Huber and includes a diaphragm having radial fuel inlets and communicating through the tube 7 shown in Fig. 1 with the bottom interior part of the fuel tank S. The interior o-f this tank is divided into two chambers by an inclined wall 9 formed with an opening 10 passing therethrough. The lower chamber contains the liquid fuel while the upper chamber serves as a condensing space which communicates with the interior of the combined supply and mixing tube 4 through the tube 6.

A nozzle 11 communicates coaxially with the interior of the lower end portion of the supply tube 4, and this nozzle communicates with a hand pump 14 through conduit 12 and non-return valve 13 which prevents air from flowing from conduit 12 into the hand pump 14. A branch 12a of conduit 12 leads into the upper chamber of the tank 8. Furthermore, the supply and mixing tube 4 carries a spark plug 15 which communicates with the interior thereof, this spark plug being electrically connected by a suitable lead 16 with an electrical ignition apparatus 17 of any known structure. Thus, the ignition apparatus 17 includes in a known way an ignition coil in the form of a transformer whose primary winding is supplied with electricity by a small drive battery communicating electrically with the primary winding through a switch 18 and an automatic interrupter switch. The secondary winding provides the spark potential for the spark plug 15.

In order to start the pulse jet engine described above, the operator closes the switch 18 so that sparks jump across the gap of spark plug in quick succession. Then the operator operates the hand pump 14- to supply air through conduit 12, 12a under pressure to the tightly closed fuel tank 8, so that air streaming through the tube 6 sucks into itself a rich proportion of fuel at the above-mentioned diaphragm, and this mixture flows into the mixing tube 4. In the latter this mixture mixes with the air entering the tube 4 through the nozzle 11, and the resulting mixture then becomes ignited by the spark plug 15 into a luminous continuously burning flame which enters from tube 4 tangentially into combustion tube 3 and heats the wall thereof.

As is well known, such Ia luminous flame does not provide complete combustion of the fuel air mixture, and therefore unburned combustible components (particularly CO) circulate within the cyclone-formed combustion tube 3 before reaching the exhaust tube 1. As soon as a part of the Wall of tube 3 glows these cobustible gas components which enter the tube 3 become ignited and the first explosion takes place within the combustion tube 3, this explosion providing a sudden blast of exhaust gases through the tube 1 in the direction of arrow A. After a few seconds these explosions follow each other uniformly and a resonant intermittent combustion takes place, providing furthermore an automatic suction of fuel through the tube 6 and air through the non-return valve 5, asis described in great detail in U.S. Patent No. 2,719,580 and in U.S. Patent No. 2,644,512 of Durr et al.

When a loud humming sound is heard, the operator knows that resonant intermittent combustion is under way and stops operating the pump and opens the switch 18, since this combustion automatically continues without artificial ignition until the closure 19 of tank 8 is opened to bring the upper chamber of this tank to atmospheric pressure.

The liquid to be atomized is stored in the tank 20 whose filling pipe 21 is tightly closed and whose interior air space communicates with the interior of combustion tube 3 through non-return valve 22 and conduit 22 which communicates at one end with valve 22 and at its opposite end with tube 4. The non-return valve 22 permits gas to flow only from tube 3 to the tank 20 so that the air space in the latter remains during operation of the engine under a pressure corresponding to that of a column of water 1 to 2 meters high. This pressure remains substantially constant during operation. As a result of this pressure the liquid in tank 20 is fed upwardly through pipe 23, valve 24, filter 25, and pipe 26 to the distributing means 2. Valve 24 is a simple shut-off valve.

The distributing means 2 is shown in Fig. 3 as including a tubular casting 30, an insert ring 31, and a front ring 32 removably joined to the ring 30 by the springy clips 33, the ring 31 being clamped between the annular members 30 and 32. The inner surface of the right end portion of tube 30, as viewed in Fig. 3 is threaded and threadedly joined to the end of the discharge tube 1. This tube 30 furthermore is formed with an axially extending bore 35 communicating with the left end face of tube 3l), as viewed in Fig. 3. The ring 31 is formed in its left face, as viewed in Fig. 3, with an annular groove 34, and furthermore only the outer periphery of ring 31 engages ring 32. The inner periphery of ring 31 is spaced from ring 32 to define with the latter an `annular gap 36 which forms van annular nozzle outlet directed toward the axis of tubes 30 and 1, these tubes being coaxial with each other. Also, as is shown in Fig. 3, the ring 31 is fonned with an opening aligned with bore 35 to form a continuation thereof and feeding into the groove 34. The gap 36 preferably has a width of approximately 0.2-0.5 mm. Through this gap the liquid to be atomized is transmitted to the pulsating exhaust gas stream A which issues from the tube 1 at a high speed. This gas stream atomizes the liquid iand carries it along in the direction of arrow A, as is described in detail in co-pending application Serial No. 281,246 of Durr et al.

The tubular casting 30 is provided with a radially extending tubular portion 37 communicating with the bore 35, and a nozzle 39 is threaded into a tubular portion 37,. The nozzle 39 is formed with `an axial bore 3S which communicates at its upper end7 as viewed in Fig. 3, with the conduit 26 and which is closed at its bottom end, as shown in Fig. 3. This bottom end of nozzle 39 is conical and completely fills a conical recess formed in tube 30, as shown in Fig. 3. Threads are providedv at the top portion of nozzle 39 for connecting the latter to the conduit 26. The nozzle 39v is formed adjacent its lower end, as viewed in Fig. 3, with radial bores 40 communicating with axial bore 38 and with bore 35 so that the fluid to be atomized passes from the conduit 26 through the bore 38 and bores 40 into the bore 35. From the latter the fluid passes into the annular groove 34 and out through the annular nozzle outlet 36.

This annular nozzle outlet 36 serves principally the purpose of providing relatively large droplets. If it is desired to obtain a mist composed of fine droplets, then the nozzle 39 of Fig. 3 is exchanged for the nozzle 39a shown in Fig. 3a. The radial bores 40 are omitted from the nozzle 39a, and instead its axial bore is open at its bottom end 41 to feed the liquid directly into the interior of tube 30. The liquid to be atomized then flows through nozzle 39a directly into the exhausting gas stream without reaching the annular channel 34. If desired a third nozzle may be provided having an axial bore corresponding to that of nozzle 39a and in addition the radial bores 40 of nozzle 39 so that the liquid to be atomized is distributed partially directly into the exhausting gases through the nozzle -outlet 41 and partially into the exhausting gases through the gap 36.

Inasmuch as the temperature of the exhausting gases is very high, it is desirable to cool the same. For this purpose the pulse jet engine 1, 3 is fixed within a tubular jacket 51 which is joined to the engine by ribs 50 fixed to the inner surface of jacket 51 and the outer surface of combustion tube 3. This jacket 51 is spaced from and coaxial with tubes 1 and 3, completely surrounding the latter and extending along the former almost up to the outlet end thereof, as indicated in Fig. 1. Both ends of jacket 51 are open. The tubular jacket 51 isin turn fixed within a second, shorter tubular jacket 53 by ribs 52 which are fixed to the outer surface of jacket 51 and the inner surface of jacket 53. This latter jacket is coaxial with jacket 51, completely surrounds combustion tube 3, and extends part Way along discharge tube 1, the forward end of the outer jacket 53 being open. The jacket 53 extends rearwardly beyond jacket 51 and is closed at its right end portion, as viewed in Fig. 1, with a pair of axially spaced walls 54 and 55. In order to draw through these jackets fresh air which will cool both combustion tube 3 and discharge tube 1, the right end wall of the combustion tube 3, as viewed in Fig. 1, is connected to a second discharge tube 56 which communicates through this end Wall with the interior of combustion tube 3, at the axis thereof. The discharge tube 56 is of an appreciably smaller diameter than discharge tube 1 and curves from combustion tube 3 around to the left, as viewed in Fig. 1, to extend to the left along the annular space between jacket 51 and tubes 1 and 3. The outlet end of discharge tube 56 is located a relatively short distance to the rear of the left open end of jacket 51, as viewed in Fig. l. The discharge tube56 forms in this way together with jacket 51 an ejector so that the gas pulsating out of tube 56 in the direction of arrow B of Fig. 1 creates a partial vacuum in the annular left open end of jacket 51, as viewed in Fig. 1, to draw air out of the interior of jacket 51.

Both of the end walls 54 and 55 of jacket 53 are formed with apertures 57 and 58, respectively, and these apertures are out of alignment so that air passing through these apertures into the jacket 51 is compelled to take the circuitous paths indicated by the arrows C in Fig. l. Thus, the arrangement of apertures 57 and 58 provides a substantial resistance to the flow of cooling air through the walls 54 and 55, and therefore part Aof the cooling air drawn into the jacket 51 through its right open end, as Viewed in Fig. 1, is obtained through the left open end of the outer jacket 53, this latter cooling air flowing in the direction of arrows D of Fig. 1 into jacket 53 land along the latter to the right where this air then changes its direction and moves to the left Within the jacket 51. f

As is apparent from Fig. l, the hand pump 14 is fixed by suitable ribs to the outer surface of the outer jacket 53.

The parts 1, 3, 4, and 56 of the above described structureare preferably made of nickel-molybdenum-steel alloy which has a high resistance to heat and ignition. The jackets 51 and 53 and all other parts of the apparatus may be made of aluminum so that the entire apparatus is light enough to be comfortably carried about by the operator. The pump 14 serves additionally as a hand grip, and for convenient handling of the appa- Y ratus a shoulder strap 59 may be connected to the pump 14, as shown in Fig. 1.

The cooling air flowing through the jackets 51 and 53 cools the exhausting gases sufficiently to provide at the discharge means 2 an exhaust gas temperature of a few hundred degrees centigrade. Thus, the liquid to be atomized which is introduced into the exhausLing gases through the annular gap 36 is not heated to an undesirable degree during atomization. Inasmuch as the surface tension of most liquids decreases with increasing temperature, it is desirable to guide at least a part of conduit 26 helically about jacket 51 in the manner illustrated in Fig. l, so that the liquid to be atomized is slightly preheated on its way to the distributing means 2.

The structure shown in Figs. 1-3 sprays the liquid stored in tank 20 in the form of relatively large droplets having a diameter of approximately 0.2 mm., as is required for spraying fruit trees, for example. In order to provide finer droplets or denser mists attachments 60-61 shown respectively in Figs. 4aand 4b may be mounted on the jacket 51.

The attachment 60 shown in Fig. 4a is in the form of a tubular extension overlapping the left free end of jacket 51, as viewed in the drawings, and extending forwardly therefrom through a substantial distance beyond discharge means 2, as indicated in Fig. 4a. In order to place tubular extension 60 on jacket 51, the nozzle 39, or 39a, is removed from tube 30. Then the extension 60 is placed on the end of the jacket 51. The extension 60 is formed withan opening which is aligned with the tubular extension 37 of tube 30, and the nozzle 39 or 39a is then insertedk through this opening back into threaded engagement with extension 37, so that the nozzle 39 or 39a additionally serves the purpose of ypreventing axial and angular movement of extension 60 with respect Yto the jacket S1. By means of the tubular extension 60, the cooling air which is heated within jacket 51 is directed to the space just ahead of the discharge means 2 so that 'the droplets formed by the exhausting gas stream A must first be-driven through the hot air zone located in extension 60 before reaching the outer atmosphere. In this way, the droplets are'heated to anappreciably greater degree so that they boil and become brokenrup into finer droplets. When extension 60 is used with nozzle 39, the'apparatus provides a lmist composed partly of relatively largeand partly of tine droplets, so that the cornbination of elements 60 and 39 with the remainder ofthe disclosed apparatus is particularly suitable for 'combating insects with DDTsince the larger droplets quickly form a good coating which sticks to the leaves of the sprayed plants while the finer droplets find their way Iinto the calyxesof the plants. If nozzle 39a is used with eXtension v60, instead of nozzle 39, then the proportion of n'e droplets is increased to such a great extent that a very dense mist is'provided which may be carried by air currents all the way up to Vthe tree tops and which encounters and kills insects even in flight. These fine droplets have an average diameter of approximately 20-50 microns.

The extension 6 1 of Fig. 4b may be mounted on and removed from jacket 51 in the same way as extension 60. It will be noted that extension 61 is considerably longer than extension 60 so that the above described results produced by extension 60 are produced to a greater degree' with extension 61. Thus, with this extension it is possible to provide an extremely dense mist which re- Ymains suspended in the air for hours and which is composed of droplets having an average diameter of approximately lO microns. Thus, the extension 61 is particularly suited for laying mists which surround plant cultures to protect the latter from frost.

Inasmuch as the tank 20 may contain the most varied chemical solutions or emulsions and inasmuch as the structure of the invention may be used as desired with or without attachments 60 and 61 and with nozzle 39 or nozzle 39a, the structure of the invention provides an aid to the farmer which can replace all of the various devices used for different purposes mentioned above up to the present time, and furthermore the structure of the invention is o-f an extremely light weight and may be handled without any inconvenience or discomfort.

The attachment illustrated in Fig. 4c makes it possible to vuse the structure of the invention as a flame thrower forsrnokng out wasp nests and for thawing frozen pipes and the like. This attachment of Fig. 4c includes a tubular extension 62 similar to extension 60 and removably mounted on jacket 51 in the same way. A tube 64 of a larger diameter than extension 62 and having an open left end, as viewed in Fig. 4c, is fixed to extension 62,`surrounds the left open end portion thereof, as viewed in Fig. 4c, and is formed with openings 63 in the region with the fresh air sucked in through the openings 63 to form a combustible mixture which may be easily ignited `at the outlet of tube 64 with a suitable fuse in order to .provide a roaring, very hot iiame F just ahead of the ytube 64. With this arrangement it is possible to provide a heat output of up to 150,000 kcaL/h. When the noz*- zle 39 is used with the attachment of Fig. 4c, the ame F yis luminous, while when the nozzle 39a is used with the attachment of Fig. 4c the flame is almost blue, so that the device may then be used by the farmer as an aid in quickly lproviding aV fire suitable for forging.

It will be understood that each of the elements described above, or two or more together, may also find `a useful application in other types of pulse jet engines differing from the types -described above.

While the invention has been illustrated and described as embodied in atomizing pulse jet engines, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying currentrknowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed is:

.1. In a pulse jet engine, in combination, wall means rdefining a combustion chamber for the engine; a first discharge tube communicating with said combustion chamber' for discharging gases therefrom; a supply tube communicating with said combustion chamber for supplying a combustible mixture thereto; a tubular jacket having an open end and surrounding said combustion chamber land at least the part of said first discharge tube adjacent said combustion chamber; and a second discharge tube 'communicating with said combustion chamber, extending between said jacket, on the one hand, and said first dis- Echarge tube and combustion chamber, on the other hand, 'and having adjacent said open end of Said jacket between said open end of said jacket and said combustion chamber I a discharge end directed in the same direction as said open end of said jacket.

2. In a pulse jet engine as defined in claim l, said first and second discharge tubes respectively communicating with opposite ends of said combustion chamber and said second discharge tube curving from said combustion fchamber and extending alongside of the latter and said iirst discharge tube for directing discharge gases in the ;same general direction as said first discharge tube.

3. In a pulse jet engine as defined in claim 1, a second j tubular jacket connected to, at least partly surrounding, .and spaced from said first-mentioned jacket, said second jacket having an end wall distant from said first discharge tube.

4. in a pulse jet engine, in combination, a combustion bustible mixture thereto; a first tubular jacket having opposite open ends, said'jacket,beingconnected to one of y said combustion and discharge tubes and spaced from both of said tubes, said jacket surrounding said combustion tube and at least the part of said first discharge tube adjacent said combustion tube; a second discharge tube communicating with said combustion tube, extending between said first Vjacket and said first discharge tube; and a second jacket connected to, spaced from, Vand at least partly surrounding vsaid first jacket, said second jacket having an open end portion thereof surrounding a part of said first jacket ywhich is located about said first discharge tube and having `an opposite end portion located beyond said first jacket; and a pair of axially spaced walls fixed to and extending across said latter end portion of said second jacket,- said walls respectively being formed with apertures which areout of line with each other.

5. In a pulse jet engine, in combination, wall means ldefining a combustion chamber for the engine; a first discharge tube communicating with said combustion chamber for discharging gases therefrom; a supply tube communicating with said combustion chamber for supplying a combustiblemixture thereto; a first tubular jacket having opposite open ends and surrounding said combustion chamber and at least a`partof said first discharge tube adjacent said combustion chamber; a second discharge tube communicating with said combustion chamber, extending between said first jacket and said first discharge` tube and having a discharge end located adjacent and directed toward one of said open ends of said first jacket between said one open end of said first jacket and said combustion chamber; and asecond jacket connected to, spaced from, and at least partly surrounding said first jacket, said second jacket having an open endV at a portion thereof surrounding a part of said first jacket which is located about said first discharge tube and having an opposite end portion beyond said first jacket; and means carried by the latter end portion of the Said second jacket for providing a restrictedflow of air into said second jacket through said opposite end portion thereof.

6. In a pulse jet engine, in combination, wall means defining a combustion chamber; a supply tube communicating with said combustion chamber supplying a combustible mixture thereto; a discharge tube communicating with said combustion chamber and having an open discharge end distant from Said combustion chamber; a jacket tube having one open end directed in the same direction as said discharge end of said discharge tube, said jacket tube surrounding said combustion chamber and at least a portion of said discharge tube adjacent said combustion chamber, said jacket tube having an opposite end providing a restricted iiow of air into said jacket tube; and a seconddischarge tube communicating with said combustion chamber and extending along the space between said jacket tube and first-mentioned discharge tube, said secondv discharge tube having adjacent said one end of said jacket tube between said one end of said jacket tube and said combustion chamber a discharge end directed in the same direction as said one end of said jacket tube and said discharge end of said first-mentioned discharge tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,300,823 Dickey Apr. 15, 1919 2,029,337 Parker Feb. 4, 1936 2,522,945 Gongwer Sept. 19, 1950 2,525,782 Dunbar Oct. 17, 1950 2,634,804 Erickson Apr. 14, 1953 2,643,107 Kamm June 23, 1953 2,695,053 Huber Nov. 23, 1954 2,707,515 Lafferentz Mayl 3, 1955 2,715,436 Lafierentz Aug. 16, 1955 FOREIGN PATENTS )1,053,662 France Sept. 30, 17953 

